Why Are My .223 Loads So Much Slower Than The Chart?

[UtopiaTexasG19]

Until I get a chance to buy in some different recommended powders for the
.223 such as Varget and the IMR 8208 I have been trying out some H4895 I have on the shelf but my loads are comming out averaging 450-550 fps slower than the Hodgdon charts depending on the charge. I am using the exact new Winchester casings fully sized and checked for lenght, the exact 55gr. Sie SP bullets and exact Winchester SR primer. I also have the lenght at 2.200" as per the chart. I believe that my chronograph is working properly as it is consistant with fps and my electronic weigh scale for powder checks out perfectly so I am at a loss why these test rounds are so much slower than the Hodgdon chart. These rounds in fps are in the same general fps area as some cheap Wolf and Brown Bear I borrowed from a neighbor. The only difference I can see is that the Hodgdon chart states a 24" barrel was used and mine is a 16". Could the barrel lenght make that much of a difference? BTW-These rounds are super accurate in my .223 and I am shooting 3" groups at 50 yards with iron sights. For my poor shooting abilities this is phenominal! :)

[DragoonDrake]

The general rule of thumb is 75fps per 1'' of barrel. So 8'' x 75fps = 600 fps. I would say you are in the right ball park.

[btroj]

Yes, barrel length makes a difference. 2 inches can make a significant difference, the 8 inch difference you have is huge. Think about it- your barrel is only 2/3 the length of that used by the powder company.
You can't get 24 inch barrel velocities in a 16 inch barrel. At least not safely. Your gun has traded velocity for the "mobility" of a shorter barrel. This happens with lever actions with short barrels for woods hunting too.
If you have accurate ammo then ignore the velocity. If you want the velocity then get a 24 inch barrel.

Welcome to the world of trade offs.

[captaint]

Utopia - With 8" barrel length difference, that's where my money is going on your 400 or so FPS spread. There are other factors, but that's the most obvious. enjoy Mike

[Larry Gibson]

Yup, 8" less barrel is a pretty good indicator......

Larry Gibson

[Lizard333]

Another example:
I was getting some slow reads on my security 6, 4 inch barrel. Shot the same loads in my security 6 with a 6 inch barrel, got the loads to match the data in the reloading manual. I had the same brain fart you did even though I knew better. In pistols the effect is even greater as in some cases the powder hasn't even finished burning as the bullet is already leaving the barrel. When you look at your relaoding data it is imprtant to try to repolicate the original testing done with the load you are using, as it makes a big difference in the performance of the load you are shooting.

[leadman]

The powder companies also list muzzle velocities, while most chronographs are set up at around 15 feet. There is a formula to calculate the muzzle velocity from a chronograph reading but I can't find it now.
Having shot a 14" Contender in 223 for many years your readings are where they should be.

[Bret4207]

Also, a 16" barrel .223 sounds like it might be an AR. Some of your gas pressure is going to cycle the action, how much I don't know, and that powder co test might well have been done in a Universal Receiver which has no "give" to it. That might affect it too. But 99% of it is barrel length.

[UtopiaTexasG19]

Thanks for the information. Here are some other interesting replys...
http://thefiringline.com/forums/showthread.php?p=4758731#post4758731

[firefly1957]

here is a link to a group that cut a barrel down to find out the difference it looks like 400f/s is
About right.
http://www.accuratereloading.com/223sb.html

[leftiye]

Short answer - the chart lied.

[MtGun44]

The chart was for a 50% longer barrel!

Bill

[1Shirt]

Charts are guides, and are printed based on specifics for given bbls. Variation from the given bbls will definately result in changes, and shortening will result in lesser vols.
1Shirt!:coffeecom

[rond]

Hodgon uses longer barrels for their data, I really liked the velocity of the .357 loads until I saw that it was for a 10 inch.

[LAcaster]

A M-4 AR is a close quarters battle rifle, at room distance 500fts makes no difference. If you want long range accuracy get a 338 Lapaua. Both are equal at the job they were assigned,

[Larry Gibson]

A M-4 AR is a close quarters battle rifle, at room distance 500fts makes no difference. If you want long range accuracy get a 338 Lapaua. Both are equal at the job they were assigned,

It's the distance between "room distance" and 300+ meters(long range these days) that the M4 is failing to provide adequate "stopping power" at with the reduced ballistics of the shorter barrels. It's why I kept my 20" barreled M16A2 instead of taking an M4 that every one wanted to give me in Iraq. Told them I take an M14 though.........

Larry Gibson

[303Guy]

There is a formula to calculate the muzzle velocity from a chronograph reading but I can't find it now.Try this link - it does it for you.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

[Doc Highwall]

I would like to mention the burn rate of the powder.

My 308 win was slow with the lot of AA5744 that I was using but when I changed the Burn Rate Factor in Quick Load I had better predictions of what a charge would do and was able to use this for other cartridges with this lot of powder.